Color encoded hologram playback apparatus

ABSTRACT

A hologram record is made containing information representative of the color and brightness of a scene. A replica of the hologram is played back in a system including a laser imaging unit for producing brightness and color representative signals which may be applied to a display device for reproducing the scene in its original colors.

.JM RJ J B I L) o [1 llnrle Gorog COLOR nnconnn HOLOGRAM PLAYBACKAPPARATUS [45] Dec. or, raw

Primary ExaminerRichard Murray Attorney, Agent, or FirmE. M. Whitacre;William H.

[75] Inventor: lstvan Gorog, Princeton, NJ. Meaghan P l Rasmussen [73]Assignee: RCA Corporation, New York, NY.

[22] Filed: Sept. 27, 1973 21 Appl. No.: 401,232 57 ABSTRACT Related US.Application Data [62] Division of $61. No. 880,680, Nov. 28, 1969, Pat.No. A hologram record 15 made comalmng mformatlon 3,790,701.representative of the color and brightness of a scene. A replica of thehologram is played back in a system [52 us. or. 358/2, 350/35 includinga laser imaging unit for producing brightness [51] Km. Cl. H0411 9/02and l r r pr nta ive ignals which may be applied 58 rind of Search178/52, 5.4; 350/35 to a p y device for reproducing the Scene in itsoriginal colors. [56] References Cited UNITED STATES PATENTS 3 Claims, 6Drawing Figures 3,506,327 4/1970 Leith et al. 350/35 64 89 1 y; 6; /Z//:i I i M i l m; l l t 0- 455 10-!455 HATE/r 2 H175? 04mg fl-JMAZDEI'EU/WK 95756778 d2 .swz .rr/az M on; Mar Y 5-) fit OR mi 35312 COLORENCODEI) IIOLOGRAM PLAYBACK APPARATUS This application is a division ofmy copending application, Ser. No. 880,680, filed Nov. 28, 1969, now US.Pat. No. 3,790,701, and particularly relates to apparatus for playingback color encoded hologram records.

BACKGROUND OF THE INVENTION The term light, as used herein, includeselectromagnetic radiation having a wavelength within the spectrumextending from infrared through visible to ultra violet. The termmonochromatic light as used herein means light composed substantially ofa single wavelength. Spatially coherent light, as used herein, meanslight emanating actually or apparently from a point source.

A hologram is a recording of all the information in a wave front oflight obtained from an object which is illuminated with spatiallycoherent monochromatic light, rather than an image of the objectobtained in ordinary photography. More specifically, as described indetail in the article, Photography by Laser, by M. N. Leith and JurisUpatnicks, appearing on Page 24 of the June 1965 issue of ScientificAmerican, a hologram consists of the recording of the interferencefringes in a wave front covering a given area resulting from theinterference between a first component of light obtained directly from aspatially coherent monochromatic originating light source, which firstcomponent is directed to the given area at a predetermined angle withrespect thereto, and a second component of light obtained from theobject to be recorded which is illuminated by light originating from thesame light source simultaneously with the first component, the secondcomponent being directed at least in part to the given area at an angleother than the aforesaid predetermined angle.

These interference fringes result from the fact that the difference inpath length, in wave lengths, and hence the difference in phase, betweenthe first or reference component of spatially coherent monochromaticlight and the second or information component of spatially coherentmonochromatic light varies from point to point. Therefore, constructiveinterference between the two components takes place at certain pointsand destructive interference between the two components takes place atother points. Furthermore, the relative amplitude of the second orinformation component varies from point to point. This causes avariation in the contrast of the resulting interference fringes. In thismanner, the recorded interference fringes form a pattern which definesboth the amplitude and the phase ofthe second or information componentas modulations in the contrast and spacing of the recorded interferencefringes. This recorded pattern, which is called a hologram, contains allthe information that can be carried by light waves transmitted through,reflected or scatteredfrom an object.

A replica of the wave front which comprises the second or informationcomponent may be reconstructed by illuminating a hologram with a sourceof spatially coherent monochromatic light. In this case the hologramdiffracts light impinging thereon to form two sets of first-orderdiffracted waves each of which is representative of the waves thatissued from the original object. One of these two sets produces avirtual image of the original object, while the other of these two setsproduces a real image of the object without the use of a lens. Thevirtual image is in all respects like the original object, and if theoriginal object were three dimensional, the reconstructed virtual imageshows depth and gives rise to parallax effects between near and farobjects in the scene in the same manner as did the original object. Thereal image, however, is pseudoscopic, i.e., its curvature is reversedwith respect to the original object, convex regions appearing to beconcave, and vice versa.

Another property of a hologram is that the entire image is reproduced inresponse to the illumination of any portion of the hologram regardlessof how small the size of'this portion. However, as in the case ofapinhole camera, resolution is lost and the depth of focus becomes largeras this portion is made smaller, since these are functions of theaperture of the imaging system. The reason for this property ofholograms is that each point on the hologram receives light from allparts of the original object and therefore contains, in an encoded form,the entire image.

Normally, a hologram is recorded on a silver emulsion photographicplate, the pattern of interference fringes thereof being manifested byvariations in the opacity of the developed plate. However, it has beenfound that the thickness of the emulsion of a developed hologram plateis a linear function of opacity of the emulsion. Thus, the pattern ofinterference is also manifested by a relief pattern with respect to theground of the emulsion surface which is made up of a plurality ofprofile contours the relative position and relative magnitude of whichmanifest the hologram information. Such a relief pattern may beemployed, independently of any difference in opacity of the photographicplate, in the reconstruction of the hologram information.

More particularly, the silver in the emulsion may be bleached out,leaving a transparent photographic plate having the hologram informationrecorded thereon both in the form of the aforesaid relief pattern, andin the form of variation in refractive index corresponding spatiallywith the aforesaid relief pattern. Considering only the aforesaid reliefpattern, since the index of refraction of such a transparentphotographic plate is different from air, when a spatially coherentmonochromatic beam of light shines through such a plate, light emergingfrom thicker portions of the plate will be phase delayed relative tolight emerging from thinner portions of such a plate by an amount whichis proportional to the difference in thickness therebetween. These phasedelays, varying from point to point in accordance with the aforesaidhologram relief pattern, result in diffraction taking place which isidentical to that obtained from a difference in opacity of the plate.Therefore, a reconstructed wave front will be formed. Furthermore,rather than bleaching the silver from the emulsion, the emulsion mayhave a thin reflective metal film deposited thereon, which faithfullyfollows the contour of the relief pattern. In this case, a beam ofspatially coherent monochromatic light reflected from. the reliefpattern appearing on the metalized surface of the plate causes arelative phase delay between light reflected from relatively higher andlower points of the relief pattern. This also results in a reconstructedwave front being formed by diffraction. A hologram which has itsinformation manifested by a relief pattern of interference fringes or byvariations in refractive index, rather than by a pattern of varyingopacity is called a phase hologram.

It will be seen that a phase hologram, in the first instant, need notnecessarily be prepared from a silver emulsion photographic plate. Photoresist materials and techniques, well known in the art, may bealternatively employed in preparing a phase hologram. Also techniquesfor recording on thermoplastic materials may be employed for preparing aphase hologram. In fact, photoresist materials and thermoplasticmaterials have higher resolution capabilities than does a silveremulsion photographic plate.

As taught in a copending application Ser. No. 509,100 entitled HologramRecord Pressings filed on Nov. 22, 1965 by Hendrik J. Gerritsen andDavid F. Greenaway, phase holograms may be utilized as master records,similar to master phonograph records, for mass producing duplicatehologram recordings or pressings in the same or a similar manner andemploying the same or similar techniques as utilized by the prior art inmass producing duplicate phonograph records from master phonographrecord's. As disclosed by Gerritsen et al. the master phase hologramrecording may be made on any of several recording media, the essentialrequirements of the recording medium being that it is dimensionallystable and that it can be impressed with a relief pattern for formingthe hologram record. Once the master hologram record in relief patternform is produced it is then covered with a thin metal coating by meanssuch as evaporation, after which the same techniques normally employedin making duplicate phonograph record pressings or replicas from amaster phonograph record may be employed in making duplicate hologramrecord pressings or replicas from the master hologram recording inrelief pattern form.

Gerritsen et al disclose how the hologram master may be used to impressthe relief pattern on clear vinyl which in one form, may be in discform, the individual hologram relief patterns forming a spiral recordingon the disc.

The apparatus described in the Gerritsen et al application is useful inmaking hologram replicas of transparencies or motion picture film. Thereplicas are cheaper than conventional motion picture film replicascontaining the same information.

Gerritsen et al describe a method of making a hologram replicacontaining color information. In order to convey red, green and blueinformation of a color scene contained in a single frame of color motionpicture film or a single color transparency, Gerritsen et al record eachcolor in a separate hologram on the disc replica. Thus, three hologramsare required to record the color content of the color film frame orcolor transparency. Likewise, in the playback system described byGerritsen et al. three image pickup tubes, such as utilized intelevision cameras, are utilized to pickup the separate red, green andblue information from the three separate holograms in order to providesimultaneous color representative signals which may be applied to acolor television display tube for reproducing the original color scene.

An object of this invention is to provide apparatus for producing colorand brightness representative signals from a single frame of a colorencoded hologram recording.

In accordance with the invention of my copending parent application,Ser. No. 880,680, a method is provided for producing a color encodedhologram record by encoding brightness and color repesentative signalsrepresentative onto black and white film and making a relief pattern ofa hologram of the color encoded film on a record medium.

A system is provided for producing a color encoded hologram. Means areprovided for combining signals contained within different frequencyranges representative of the color and brightness ofa scene for forminga composite color and brightness representative signal. The compositesignal is coupled to means for recording the composite signal on blackand white film for making a color encoded film record of the color andbrightness representative signals. The encoded film record is utilizedin hologram record producing means for forming a hologram in a recordingmedium which hologram is representative of the color encoded film image.

In another embodiment of the invention of my aforesaid parentapplication a color transparency or motion picture film is encodeddirectly onto black and white film by optical color encoding filtermeans disposed between the illuminated color transparency or motionpicture film and the black and white film. The developed black and whiteencoded film is then utilized in hologram record producing means forforming a hologram in a recording medium which hologram isrepresentative of the color encoded film image.

In another embodiment of the invention of my aforesaid parentapplication color and brightness information is encoded directly ontothe hologram. Color separation negatives made from a color transparencyor color motion picture film and having superimposed grating patternsare disposed in the information beam path of a source of spatiallycoherent monochromatic light in the hologram producing apparatus wherebythe color encoding and hologram forming is accomplished simultaneously.

A color encoded hologram record is provided containing in relief patternform a color encoded hologram representative of the color and brightnessof a scene.

In accordance with the principles of the present invention, a system isprovided for playing back a replica of a color encoded hologram forproducing color and brightness representative signals. Laser imagingmeans directs spatially coherent monochromatic light through a replicaof a color encoded hologram. A reconstructed color encoded image isformed on the photosensitive element of an image pickup tube. Scanningof the image produces a composite signal representative of the color andbrightness of the' encoded scene contained in the hologram replica. Thecomposite signal is applied to means for separating the color andbrightness signals for producing separate color and brightness signalsrepresentative of the encoded scene and suitable for application to adisplay device for reproducing the encoded scene in its original color.

Particular objects and advantages of the present invention will beappreciated by those skilled in the art upon'a reading of the followingdetailed description and an inspection of the accompanying drawings inwhich:

F l0. 1 is a general system block diagram of apparatus for producing andplaying back color encoded holograms;

FIG. 4 is a functional diagram of apparatus for making hologram recordsof color encoded film;

FIG. 5 is a functional diagram of apparatus for making color encodedhologram records of color separation negatives; and 7 FIG. 6 is afunctional diagram of apparatus for producing color and brightnessrepresentative signals from color encoded hologram records.

DESCRIPTION OF THE INVENTION FIG. Iis a general system block diagram ofapparatus for making and playing back color encoded holograms.

A source 10 of color images or color signals is provided. Color imagesmay be provided by illuminating color transparencies on color motionpicture film. Electrical signals representative of the color andbrightness components of a scene may be provided, for example, by anysuitable color television camera or a tape machine providing color andbrightness representative video signals. The color images or electricalcolor signals from source 10 are coupled to color encoding means 11. Inthe case in which color images are utilized, color encoding means 11optically encodes the color images by means of color encoding filters.The encoded images may then be recorded on black and white film. Whenelectrical color and brightness representative signals are utilized,color encoding means 11 electrically encodes the signals as modulationof carrier waves. The modulated carrier waves may then be recorded onblack and white film. Examples of apparatus for optically andelectronically encoding color information will be describedsubsequently.

The color encoded information, which may be on black and white film, isutilized in hologram making means 12 for forming a color encodedhologram on a recording medium. The recorded hologram is processed toyield a metal master recording which is then utilized to produce manyinexpensive hologram replicas. A color encoded hologram replica is thenplayed back in a color encoded hologram playback means 13 for producingelectrical signals representative of the color and brightness of thecolor encoded scene. The electrical signals are coupled to a displaymeans 14 which may be a color television picture tube, for example, forreproducing the encoded scene in its original colors.

FIG. 2 is a functional block diagram of apparatus for encodingbrightness and color representative signals onto black and white film. Asource of video signals provides a brightness signal and R (red) and B(blue) color signals. Source 20, for example, may be a color televisioncamera or a color videotape machine. The brightness or luminance signalobtained from source 20 is coupled to a low pass filter 21 whichbandpass limits the luminance signal to 3 MHz. This bandpass limitedluminance signal is coupled to an input terminal of signal adder 22.

The red color signal obtained from source 20 is coupled to an inputterminal ofmodulator 24. An oscillator 23 provides a 5 MHz carrier wavewhich is coupled to another input terminal of modulator 24. The redcolor signal amplitude modulates the 5 MHz carrier wave for I producinga red color modulated carrier wave and associated sidebands. The colorsignal obtained from modulator 24 is coupled to a bandpass filter 25which bandpass limits the red color modulated carrier wave and itssidebands to a frequency range of 4.5 5.5 MHz. This band limited redcolor representative signal is coupled to an input terminal of signaladder 22.

The blue color signal obtained from source 20 is coupled to an inputterminal of a modulator 27. An oscillator 26 provides a 3.5 MHz carrierwave which is coupled to another input terminal of modulator 27. Theblue color signal amplitude modulates the 3.5 MHz carrier wave forproducing a blue color modulated carrier wave and associated sidebands.The color signal obtained from modulator 27 is coupled to a bandpassfilter 28 which bandpass limits the blue color modulated carrier waveand 'its sidebands to a frequency range of 3 to 4 MHz. This band limitedblue color representative signal is coupled to another input terminal ofsignal adder 22. Signal adder 22 combines the luminance signal, the redcolor signal and the blue color signal to form acomposite signalrepresentative of the color and brightness of a scene.

This composite color and brightness signal is coupled to a controlelectrode of a cathode ray tube 29. The

. composite signal modulates an electron beam in cathode ray tube 29such that the image of the composite signal is displayed on a phosphorscreen of tube 29 as the electron beam scans a raster on the phosphorscreen. A film camera 30 containing black and white film records eachframe display of the phosphor screen for forming a color encoded blackand white image on the film.

A system for encoding colorand brightness signals on black and whitefilm similar to the arrangement shown in FIG. 2 is described in US. Pat.No. 2,736,762 entitled Recording of Colored Images, granted to R. D.Kell on Feb. 28, I956. The film encoded in the manner described aboveand in the Kell Patent is suitable for use in the system for making ahologram recording described in conjunction with FIG. 1.

FIG. 3 is a diagram showing apparatus for optically encoding colorinformation onto black and white film. A light source 31 is energized bya battery 32. Light from source 31 is collimated by a collimating lens33 and illuminates a color transparency 34. Transparency 34 may be asingle color slide or a frame ofa color motion picture film. It is to beunderstood that conventional apparatus is provided for advancing thecolor motion picture frames so that successive frames may be encoded. Anoptical color encoding filter assembly 36 is disposed adjacent colortransparency 34 for spatially encoding the light passing therethrough.An imaging lens 37 focusses an imageof the transparency and the colorencoding filter onto a black and white film contained within a black andwhite film camera 38.

Color encoding filter assembly 36 may be any suitable assembly forencoding color information as modulation of a relatively high spatialfrequency grating structure. An example of a suitable structure isdescribed in US. Pat. No. 2,733,291 granted to Ray D. Kell on Jan. 31,I956. Kell describes a first grating comprising alternate cyan andtransparent stripes for encoding red light by the cyan stripes blockingred light and a second grating superimposed on the first comprisingalternate yellow and transparent stripesfor encoding blue light by theyellow stripes blocking blue light and passing all other colors. Theline density of the stripes of the respective gratings is different,thereby spatially separating the red and blue encoded information. Abrightness signal is contained in the average transmission of thesuperimposed gratings. Thus, the grating structure modulated by coloredlight is imaged on a photosensitive surface where the encoded image issotred as a monochromatic pattern. It is desirable to utilizesuperimposed encoding gratings in that full color and brightnessinformation may be recorded on the black and white film within camera 38by a single exposure, but a single transparency 34 may be illuminatedseveral times utilizing separate encoding gratings for encodingdifferent colors if it may be desirable to vary the exposure time orintensity for the different colors.

FIG. 4 shows in diagrammatic form apparatus for making a hologramrecording of color encoded film whereby a single hologram contains bothcolor and brightness information. A laser means 40 emits a beam ofspatially coherent monochromatic light 41. In general, the source ofspatially coherent monochromatic light need not necessarily be a laser,since initially nonspatially coherent monochromatic light, from a sourcesuch as a gas discharging lamp, can be made spatially coherent bypassing it through a small pinhole. However, the intensity of a beam oflight passed through a small pinhole is severely limited.

The beam of light 41 is passed through an aperture 42 of a mask 43 whenshutter 44 is moved away from aperture 42. Suutter 44 is operated, forexample, at a I cycle per second rate by drive/shutter motor 66 to whichit is mechanically coupled. Passing through aperture 42 the beam oflight 41 is applied to a beam splitting mirror 45 which divides beam 41into reflected beam 47 and transmitted beam 46. Beam 47 is reflectedfrom mirror 48 and is then widened into a reference beam 47 by means oflenses 49 and 52,. The beam is passed through a pinhole aperture 50 in amask 51 located between lenses 49 and 52 to provide spatial filtering ofthe beam to eliminate unwanted fringes.

Information (or object) beam 46 is widened by means of lens 55 and lens58. The beam is passed through a pinhole aperture 56 ofa mask 57 locatedbetween lenses 55 and -58 to provide spatial filtering of theinformation beam.

Beam 46 is then applied to a diffusing glass 59 for introducingredundancy into information beam 46. Redundancy of the information beamprovides the same information to appear on many areas of the hologram,thereby minimizing effects of scratches, etc., on the hologram record.

It may be desirable to replace diffusing glass 59 with a bi-dimensionalphase grating. The use of a bidimensional phase grating eliminates thepresence of unwanted speckle noise in the reproduced image of thehologram, which speckle noise is present when a small size hologram isrecorded with a diffused light information beam. A bi-dimensional phasegrating and the advantages thereof are more fully described in acopending application, Ser. No. 662,822 entitled Redundant Speckle-FreeHologram Recording Apparatus, filed on Aug. 23, 1967, by Hendrik J.Gerritsen and William J. Hannan abandoned in favor of continuationapplication Ser. No. 29,748, filed Apr. 24, 1970, now U.S. Pat. No.3,650,595, issued Mar. 21, I972. The bidimensional grating is designedto yield the maximum possible hologram redundancy consistent withpreventing spurious grating lines caused by beats between thebi-dimensional grating and the pattern of color encoding stripes presenton the black and white encoded film 60 from appearing in thereconstructed image. In this regard it is desirable to use a form ofcolor encoding in which the code stripes run in only one direction. Thisway since there is no possibility of beats between the code stripes andan orthogonal set of grating lines, redundancy can be maximized.

Another reason for using one-directional color encoding stripes is toeliminate the need for accurate frame-to-frame registration in twodirections. In this regard the color encoding filter described inpreviously mentioned US. Pat. No. 2,733,29l is ideal.

Redundant information beam 46 leaving diffusing glass 59 is applied to acolor encoded black and white film 60. Film 60 is supplied from a reel61 and is taken up on a reel 62. The drive mechanism for moving encodedfilm 60 is coupled to drive/shutter motor 66. Color encoded film 60 isof a type produced by the apparatus described in conjunction with FIGS.2 and 3. The information beam 46 passing through encoded film 60 isapplied-to a lens 63 which has it focal point in the plane of film 60therefore, the rays of light of beam 46 emitted from lens 63 aresubstantially parallel. This arrangement of lens 63 enables productionof a Fraunhofer hologram. A phase hologram of the Fraunhofer type isadvantageous in that replicas of the hologram may be played back withthe replica in motion and still result in an image which does not moveas the hologram replica is moved across the playback light beam.

Information beam 46 and reference beam 47 are directed through anaperture 53 in a mask 54 to form a hologram on recording medium 64. Aspreviously described, information beam 46 and reference beam 47 form aninterference pattern in accordance with the information contained in aframe of color encoded film 60. This interference pattern is recorded onrecording medium 64. In this embodiment recording medium 64 is in a discform such as described in the abovementioned Gerritsen et al copendingapplication.

The disc 64 is rotated and moved vertically simultaneously by amechanism 65 coupled to drive/shutter motor 66 such that the singlecolor encoded holograms of each frame of film 60 are recorded in aspiral on recording disc 64. Thus, disc 64 after processing has recordedon it in relief pattern form holograms representative of the colorencoded images of film 60. As described by Gerritsen et al, a metalmaster may be made from recording disc 64 and utilized for producingreplicas of the original disc 64.

FIG. 5 is a diagram showing apparatus for making color encoded hologramrecords of color separation negatives. A color separation negative maybe prepared by illuminating a color transparency through a filter of aparticular color for which the negative is to be made and exposing ablack and white film with the filtered light. Those items of FIG. 5corresponding to similar items described in conjunction with FIG. 4 andperforming similar functions are designated by the same numbers as inFIG. 4.

A beam 41 of spatially coherent monochromatic light from laser means 40is directed through aperture 42 of mask 43 when shutter 44 is moved awayfrom the aperture. Beam 41 is split by mirror 45 into a beam 47 which isreflected by mirror 48 through beam widening lenses 49 and 52 and beamcontrol aperture 50 of mask 51 which spatially filters the beam,eliminating unwanted fringes. Beam 47, leaving lens 52, is the referencebeam for forming a hologram as it passes through aperture 53 of mask 54and reaches recording medium 64.

A portion of beam 41 is passed by mirror 45 for forming an informationor object beam 46. Beam 46 is widened by lenses 55 and 58 and itsfringes are controlled by aperture 56 of mask 57. Information beam 46 isdirected through glass diffuser 59 for introducing redundancy into thebeam. As described in conjunction with FIG. 4, a bi-dimensional phasegrating may be used in place of glass diffusor 59 for reducing unwantedspeckle noise in the hologram. The information beam 46 is split intothree paths by mirrors 70 and '71. Mirror 70 directs a portion of thebeam to a mirror 72. Mirror 72 directs the beam through a red colorseparation negative 73. A grating structure 74 is disposed adjacent thecolor separation negative. The grating may comprise a pattern of opaqueand transparent strips such that the light beam passing through thegrating is modulated by the information contained on the colorseparation negative 73. The information beam, containing redrepresentative information, is reflected from a mirror 75 and a mirror76 to a lens 63.

Mirror 71 reflects a portion of beam 46 to a mirror 78 which reflectsthat portion of the information beam through a blue color separationnegative 79 and a grating structure 80 disposed adjacent the colorseparation negative. Grating structure 80 has a different line densitythan grating structure 74 so that the blue modulated information has adifferent spatial frequency and is thereby separated from the red. Theblue information beam, containing modulation corresponding to theinformation contained in the blue color separation negative, isreflected from a mirror 81 and a mirror 77 to lens 63.

A third portion of information beam 46 is transmitted through mirrors 70and 71 and through green color separation negative 82. It is notnecessary that a grating structure be used with the green colorseparation negative since the red and blue information can be extractedon the basis of their respective spatial frequencies and the greeninformation will be the remainder. The green information modulated beamis transmitted through mirrors 76 and 77 to lens 63.

Impinging on lens 63 are the red, blue and green information beamportions. Lens 63 is disposed a distance equal to its focal length awayfrom the respective red, blue and green color separation negatives 73,79 and 82. Therefore, the light rays leaving lens 63 are substantiallyparallel and form a Fraunhofer hologram as the interference patternbetween the information beam 46 and reference beam 47 is established.This interference pattern, which is a phase hologram containing theencoded color information, is recorded on the recording disc 69 asdescribed in the Gerritsen et al copending application.

In the embodiment shown in FIG. it is not necessary to first separatelyencode the colors of a transparency on black and white film. Thisarrangement is advantageous in that the black and white film has anonlinear characteristic when exposed to varying intensity light whichlimits the dynamic range of the film and thereby adds an undesirablenonlinearity to a system in which nonlinearities should be minimized. Itis necessary to make color separation negatives, but this is easilyaccornplished and in the situation in which the hologram record is to beused to make many replicas, the additional cost is small when averagedover the cost of the replicas. It is to be understood that it is notnecesssary to split information beam 46 into three paths tosimultaneously illuminate all three color separation negatives, but thata single information beam path maybe through a replica of the colorencoded hologram record produced by the apparatus shown in FIGS. 2-5.The disc replica 87 is rotated and moved vertically by a mechanism 88 sothat the successive holograms on disc replica 87 are moved into theplayback beam 86. Beam 86 is directed at an angle to the plane of dischologram replica 87 so that upon reaching replica 87, a first order beam86a, produced by diffraction of beam 86 by hologram replica 87, isdirected to an imaging lens 89. Beam 86a contains the color encodedinformation and lens 89 focusses this information onto a photosensitiveelectrode 90 of an image pickup tube 911. Disc replica 87, being areplica of the redundant Fraunhofer type phase hologram recorded by theapparatus previously described, may be moved at a continuous speed bymechanism 88 without any distortion of the image formed at thephotosensitive electrode 90 of image pickup tube 91. Thus, undesiredvariations in the speed of disc replica 87 will not result in anunsatisfactory image being formed at photosensitive electrode 90.Further, the redundant hologram replica may be played at any speed,forward or reverse, since the disc speed need not be synchronized withthe scanning intervals of the image pickup tube.

The image formed at photosensitive electrode 90 will be a replica of theimage contained on the black and white encoded film or on the colorseparation negatives with the superimposed gratings previouslydescribed. As described, the encoded information is in the form of twocolor modulated carrier waves and their sidebands and a luminance orbrightness signal contained within a band of frequencies different thanthe frequency bands utilized for the color signals. Thus, this compositesignal is obtained at an output terminal 92 of image pickup tube 91 asthe electron beam scans the photosensitive electrode 98.

The composite signal obtained from terminal 92 is applied to a low passfilter 93 for separating the bright ness components from the compositesignal. Thisluminance signal having a bandwidth of 3 MHz is obtainedfrom an output terminal 94 of low pass filter 93.

The composite signal is also coupled to a bandpass filter 95 whichseparates the carrier signal modulated by blue representative signalsfrom' the composite signal. The blue modulated carrier wave is detectedby an amplitude detector 96 and coupled to an input terminal ofsubtractor 97. The composite signal is also coupled to a low pass filter98, at the output of which is obtained a luminance or brightness signalhaving a 500 KHz bandwidth, equal in bandwidth to the detected colorsignals. This narrow band luminance signal is coupled to another inputterminal of subtractor 97 in which it is subtracted from the bluerepresentative signal for producing a B-Y color difference signal.

The composite signal obtained at terminal 92 is also coupled to abandpass filter 100. Bandpass filter 100 separates the red colormodulated carrier wave and its sidebands from the composite signal. Thiswave is coupled to an amplitude detector 101 and the red colorrepresentative wave obtained from detector 101 is coupled to an inputterminal of subtractor 102. Also coupled to an input terminal ofsubtractor 102 is the narrow band luminance signal obtained from lowpass filter 98. This narrow band luminance signal is subtracted from thedetected red color representative signal for producing an R-Y colordifference signal which is obtained from an output terminal 103 ofsubtractor 102.

The brightness signal and B-Y and R-Y color difference signals may beapplied to corresponding video amplifiers in a color television receiverfor reproducing on a color picture tube an image corresponding to thescene encoded on the hologram record.

What has been described is a system and method for producing and playingback color encoded hologram records. By utilizing color encodingtechniques in making the hologram records it is possible to make anhologram record containing full color and brightness information of ascene, as represented by color transparencies or color representativevideo signals, utilizing a single source of laser light in the hologramrecording and playback apparatus. This arrangement is thus simpler andless costly than previously known arrangements requiring separate laserlight sources for recording and playing back the separate colors, eachof which were recorded in separate holograms. Also, by utilizing themethod and apparatus disclosed by applicanat it is possible to derivefull color and brightness information from the playback unit utilizingonly a single image pickup device such as a vidicon since the encodedcolor and brightness information imaged onto the vidicon may beseparated electrically with relatively simple electrical circuitry.While the invention has been described above in connection with aparticular (disc) form for the recording medium, it should beappreciated that the principles of the present invention are applicableto other recording medium forms, such as the tape form shown in theapplication of William J. Hannan, Ser. No. 862,l72, copending with myaforesaid parent application and now abandoned.

What is claimed is:

1. Apparatus for producing signals representative of the color andbrightness of a scene from a series of successive hologram records, ofimages of said scene upon each of which image is superimposed spatiallyencoded information representative of selected component colors of saidscene, said apparatus comprising:

a source of spatially coherent monochromatic light;

an image pickup device including a photosensitive electrode;

means for moving said series of hologram records in succession across anoptical path of said image pickup device;

means for directing light from said source along said optical paththrough said hologram records to form on the photosensitive electrode ofsaid image pickupv device a composite image comprising a monochromaticimage of said scene and spatially encoded color information superimposedthereon; means coupled to said image pickup device for derivingtherefrom in response to the scanning of said composite image acomposite output signal inclusive of respectivebrightness-representative and color-representative components.

2. Apparatus in accordance with claim 1 also including frequencyselective means coupled to said composite output signal deriving meansfor separately recovering the respective brighmess-representative andcolorrepresentative components from said composite output signal.

3. Apparatus in accordance with claim 2 wherein said light directingmeans includes a lens disposed in said optical path and spaced from saidphotosensitive electrode by a distance substantially equal to the focallength of said lens.

1. Apparatus for producing signals representative of the color andbrightness of a scene from a series of successive hologram records, ofimages of said scene upon each of which image is superimposed spatiallyencoded information representative of selected component colors of saidscene, said apparatus comprising: a source of spatially coherentmonochromatic light; an image pickup device including a photosensitiveelectrode; means for moving said series of hologram records insuccession across an optical path of said image pickup device; means fordirecting light from said source along said optical path through saidhologram records to form on the photosensitive electrode of said imagepickup device a composite image comprising a monochromatic image of saidscene and spatially encoded color information superimposed thereon;means coupled to said image pickup device for deriving therefrom inresponse to the scanning of said composite image a composite outputsignal inclusive of respective brightness-representative andcolor-representative components.
 2. Apparatus in accordance with claim 1also including frequency selective means coupled to said compositeoutput signal deriving means for separately recovering the respectivebrightness-representative and color-representative components from saidcomposite output signal.
 3. Apparatus in accordance with claim 2 whereinsaid light directing means includes a lens disposed in said optical pathand spaced from said photosensitive electrode by a distancesubstantially equal to the focal length of said lens.